In virtually every application in which lighting fixtures are used to produce an aesthetic effect, most notably in entertainment and display lighting, a means of selectively varying the apparent color of the light beam is required.
For this purpose, virtually every lighting fixture produced for entertainment and display applications provides some means to support a planar filter material in its beam. Beam color is changed by changing the filter material.
This filter material or "gel" generally consists of a flexible gelatin, cellulose acetate, mylar, or polyester base with a colored pigment disposed through the base or applied to it. Five major lines of flexible filter material are available, providing the lighting designer with a choice of more than 200 distinct colors. More recently, interference-type filters have been employed as well.
While the cost of the filter material itself is modest, the requirement that a change in beam color requires changing filter material has always had disadvantages in those applications which require that the color of the beam illuminating a given subject change during a performance.
One such application is the followspot. Followspots are light projectors designed for changes in beam azimuth, elevation, size, intensity, and generally shape and color, through the agency of a full time operator, traditionally located next to the fixture and actuating its beam modifying mechanisms directly by means of control levers projecting through the housing. A description of the Supertrouper followspot, for many years the standard of the industry, may be found in U.S. Pat. No. 2,950,382. In order to change beam color during the performance, virtually all followspots are provided with a mechanical color changer mechanism allowing the operator to insert any one or combination of six filters into the beam.
The applications for a mechanical method of changing filters and as such beam color during a performance are not restricted to the followspot. Without a method of changing beam color during a performance, lighting a given area of the stage in five colors during a performance generally requires the use of five fixtures, each provided with a different filter material but otherwise identical--at a very substantial increase in direct and indirect cost in fixtures, cabling, dimming, support, and control equipment, as well as the manpower required to install, adjust, and service this equipment.
It has long been apparent that if a fixture's color could be changed by remote control during the performance, that the number of fixtures required and as such the direct and indirect costs of the total lighting system could be dramatically reduced. As a result, methods of changing the color of a light source from a remote location found use with candles in the 1770s; with electric lights in the 1880s; and electrically actuated changers similar to those disclosed in U.S. Pat. Nos. 2,129,641 and 2,192,520 were in significant use in American theater by the 1930s.
The ultimate extension of the theory that a fixture with variable beam characteristics can produce a significant reduction in the size of the lighting system required to achieve a given series of effects leads us to a fixture, as disclosed in U.S. Pat. No. 3,845,351, whose every variable is adjustable under computer control, and a practical color changer is essential to its success.
And yet, despite the considerable attention paid to the design of color changers over the last half-century, no color changer mechanism yet disclosed in the art is capable of changing beam color without undesirable effects during the transition, effects whose aesthetic disadvantages represent a major impediment to the widespread adoption of such changers.
It is an object of the present invention to provide an improved color changer mechanism capable of changing beam color without undesirable intermediate effects.